SELECT 
  cscart_product_descriptions.product_id, 
  cscart_product_descriptions.short_description, 
  IF(
    cscart_product_descriptions.short_description = '' 
    OR cscart_product_descriptions.short_description IS NULL, 
    cscart_product_descriptions.full_description, 
    ''
  ) AS full_description, 
  cscart_product_descriptions.unit_name 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (
    2011, 1919, 1922, 1942, 1923, 1933, 1945, 
    1946, 1153, 1154, 1155, 2376, 2036, 
    2057, 2091, 1959, 1981, 2137, 2340
  ) 
  AND cscart_product_descriptions.lang_code = 'pl'

Query time 0.00029

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "13.31"
    },
    "table": {
      "table_name": "cscart_product_descriptions",
      "access_type": "range",
      "possible_keys": [
        "PRIMARY",
        "product_id"
      ],
      "key": "PRIMARY",
      "used_key_parts": [
        "product_id",
        "lang_code"
      ],
      "key_length": "9",
      "rows_examined_per_scan": 19,
      "rows_produced_per_join": 19,
      "filtered": "100.00",
      "index_condition": "((`cscartdevel`.`cscart_product_descriptions`.`product_id` in (2011,1919,1922,1942,1923,1933,1945,1946,1153,1154,1155,2376,2036,2057,2091,1959,1981,2137,2340)) and (`cscartdevel`.`cscart_product_descriptions`.`lang_code` = 'pl'))",
      "cost_info": {
        "read_cost": "11.41",
        "eval_cost": "1.90",
        "prefix_cost": "13.31",
        "data_read_per_join": "101K"
      },
      "used_columns": [
        "product_id",
        "lang_code",
        "short_description",
        "full_description",
        "unit_name"
      ]
    }
  }
}